help with query (delete lowest value)

i have a table with objects in categories and their positions.

there will be several rows with category 400, and they will have
various positions, i want to delete only the row with the lowest
position.

i can select the row i want to delete, but don't know how to delete
just this row.

here's my select:

SELECT * FROM categories WHERE category = 400 order by position limit 1

thanks for your help.
s7

ps - is there any cron-like facility within mysql to do this for me,
once every weekday?